Process of conditioning alpha tissue of cellulose fiber for conversion into celluloserivatives and product of same



I 677, filed October 9, 1926, t

Patented May 24, 1932 UNITED STATES PATENT; OFFICE enema A. mourns, minor: 0. serum, AND adult 11. aascn, or BERLIN, new mrsnma, assmnozas 'ro nnown comrm; or 31mm, new nmsnmn, A

CORPORATION OF MAINE PROCESS OF CONDITIONING A TISSUE OF CELLULOSE FIBER 'FOR CONVEIRISIOZN INTO- CELLULOSE DERIVATIVES AND TBODUCT OF SAME No Drawing.

This invention relates to a process of conditioning tissue of cellulose fiber for conversion into cellulose derivatives, and is, addressed more particularly to the conditioning of such material for conversion into nitrocelluloses, such as those customarily used in the manufacture of films, lacquers, artificial silk, pyroxylin products, and the like In our patent application Serial No. 140,-

here is described a process of conditioning cellulosic material for conversion into cellulose derivatives, and more especially nitrocelluloses, which comprises mechanically h drating or beating cellulose fiber prior to ormation into thin paper or nitrating tissue. Such tissue, particularly when composed of a beaten high alpha cellulose-containin wood fiber, gives a notably greater yie d of nitrocellulose. and possesses a markedly lower acid retention than tissue composed of like unbeaten fiber. In patent application, Serial No. 140,67 5, filed October 9, 1926, by Milton ().Schur and Royal H. Rasch, there is disclosed and claimed a process which comprises mercerizing the tissue prior to nitration, as mercerization or chemical hydration of the tissue fibers was found to accomplish com arable results to those accomplished by a eating or mechanical hydration of the fibers prior to formation into tissue.

We have now discovered that if a tissue of cellulose fiber, and'more especially one of high alpha cellulose wood fiber, is subjected to great pressure as by calendering or supercalendering, and" then nitrated, the hereinbefore mentioned desiderata, namely, higher yield of nitrocelluloses and lower acid retention, are attained, irrespective of whether or not the tissue is composed of beaten or unbeaten, or mercerized or unmercerized fiber. The most noteworthy improved results upon nitration are realized when a tissue composed of high alpha cellulose wood fiber is employed, but these results are representative of what happens with cellulosic fiber of other origins suitable for the preparation of nitrocelluloses. Accordingly, although the specific examples hereinafter given are concerned with a tissueof alpha wood fiber, this inven- Application filed'larch 10, 1927. -8erlal No. 174, 106.

as, "for instance, described in patent ,applica' tion, Serial No. 72,522, filed December 1,

1925, by George A. Richter and Milton 0.

Schur. Our theory is that alpha fiber, owing to its high absorptivity, is attacked rapidly by the sulphuric acid present in the mixed acid, partly dissolving or forming unstable esters, which are subsequently lost during washing and stabilizing, necessarily resulting in a low yield. Because of its high ab sorptivity, the fiber retains excessive quantities of the nitrating acid during wringing, resulting in a high acid retention coetficient. By acid retention coefiicient is meant the percentage of the weight of original nitrating acid retained by the nitrated fiber after centrifugation under carefully standardized conditions. It is a direct measure of the loss in nitrating acid experienced in usual technical practice when the centrifuged material is drowned in large volumes of cold water. When beaten or merceriz ed, however, the absorptivity and/or structure of the fiber are apparently modified to such an extent that initial attack by the sulphuric acid is retarded and the nitric acid is allowed time to penetrate into the fibers in the proper con,- centration to form stable nitrates. The present invention attains the same ends, but does so b the more simple and economical step of ca endering, which may be performed during the usual tissue or papermaking operation. If desired, calendering may be carried out in accompaniment with the improvements disclosed in the hereinbefore identified applications. For instance, as described in the first-mentioned application, the tissue may be treated with a solution of nitrocellulose or with other cellulose derivatives capable of-being regenerated into cellulose, and

t the tissue.

then, if other than nitrocellulose be employed, regenerating the cellulose in situ in This treatment may be advantageous when the tissue is formed of unbeaten or sli htl beaten fiber, as such tissue is weakan lia le to undergo disintegration or breaking during calendering. A. treatment such as described effects a permeation of the I tissue with nitrocellulose or regenerated cellulose, which encases and bonds together the fibers so that the tissue more efiectively resists disintegration or breaking durin calendering. The improvement eifecte by calendering tissue formed of well-beaten fiber or mercerized fiber, particularly the latter, is not so renounced as that effected by calendering tissue formed of unbeaten and unmercerized fiber, as .such latter tissue oifers a considerably greater-possibility of improvement.

The applicability of the present invention may best be understood by describing a specific example of procedure such as the following. A waterleaf alpha fiber tissue of about .003 inch thickness, or corresponding to a sheet of 20 pound basis weight (4802 l x36), was formed on one of the usual types of papermaking machines. The alpha fiber employe'd in the present example was beaten to a slowness of about nine minutes, and had an alpha cellulose content of about 93, a color of about 107, and a copper number of about 2.5, but it is obvious that alpha fiber of different characteristics may be employed. The sheet was dried and then compressed or condensed under very heavy pressure by passing it successively through several pairs of rolls of a supencalendering stack. Each pair of rolls comprised a hard steel, nicely finished upper roll and a fiber lower roll. The calendered dr sheet was then crimped or crinkled an out up into pieces of about onequarter inch square, and submerged for onehalf hour at 40 C. in a mixed nitrating acid bath consisting of 20.5% HNO 60.8% H SO and 18.7 H2O, the. ratio of acid to dry-tissue being 50 to 1. The nitr'ated material was then centrifuged for one minute and drowned or washed in a large quantity of cold water. The acid retention was and the 'eld of bone-dry nitrocellulose based on t e bone-dry weightof tissue was 152%. These results represent the average of a number of nitrations and indicate an increased yield and a lowered acid retention when compared to the values obtained by nitrating similar uncalendered tissue, such latter tissue resulting in an acid retention of 5.6 and a yield of 144; The viscosity of a nitrocellulose solution of the nitrocellulose prepared from the calendered tissue was 4.6, whereas this value was 2.74 when similar uncalendered tissue was used in nitration. The increased solution viscosit means an increased strength of film or at er nitrocellulose product pre ared from such solution. The results herein fore given were produced by using a fairly well beaten alpha fiber in forming the tissue. A comparatively greater improvement results when an unbeaten fiber is used in forming the tissue, as tissue composed of unbeaten fiber offers a greater op-' portunity for improvement. I

We have adverted to the fact that the tissue is crimped or crinkled after calendering. This is one of the important steps in our process, as calendering produces a smooth or glazed surface on the tissue, which tends to cause the pieces to stick together in the acid bath, to form packs or clumps, which are rather difiicult to wash free of acid. The wash water seeps in between the packed pieces rather slowly and effects only partial dilution-rather than a complete and immediate dilution of the acid retained in and between the which had been super-calendered on both,

sides and which, if crinkled, would be expected to and does give better results than a crinkled tissue calendered on only one side,

gave ayield of only 148. The acid retention was 3.3, which is less than the acid retention of tissue super-calendered on one face, showing that two-face super-calendering decreases the absorptivity of the tissue more than a single super-calendering, and also produces a betterthrowing-ofi' of acid or low acid retention upon centrifuging. Yield and acid retention, however, do not go hand in hand,

for if a sheet is insufliciently thin and is so densified or compacted that it is incompletely penetrated by the nitrating acid, the acid retention maybe quite low, but the yield is also low, owing to incomplete nitration.

The tissue may be calendered dry, or it may be moistened immediately after passage through the dry end of the paper machine, by sprinkling or spraying water thereonto as in the so-called process of water-finishing paper, or it may be steamed and then passed through the calenders, but if desired, the tissue may be only partially dried on the paper machine, and then calendered. When the tissue is calendered while moist, it ispreferably hot-calendered.

The present invention is particularly advantageous when it is desired to condition tissue for nitration without'the more expensive mercerization. A mercerized tissue is relatively slightly improved by calendering, but if desired the tissue may, in accordance with my invention, be mercerized either be fore or after calendering. A notable improvement results when tissue formed of a fairly well-beaten fiber is calendered, and

tissue formed of unbeaten fiber enjoys an" even greater relative improvement upon cal- .endering, owing to the more porous and abthat the nitrocellulose prepared'from a calendered alpha tissue yields stronger and more elastic films, lacquers, and other products than nitrocellulose prepared from similar uncalendered tissue. As stated, this is apparently a consequence of the higher viscosityof nitro-. cellulose solution producible from nitrocellulose prepared from a calendered tissue.

Heretofore, it has been thought that an uncalendered paper or tissue was best suited for nitration owing to its more absorptive con? dition, and in some cases it will be found that uncalendered paper or tissue is expressly stated to be best suited for such purpose, but so far as we are aware, we are the first to recognize and appreciate the desirability of calendering, and more particularly the calendering of a high alpha cellulose wood fiber, prior to nitratlon.

While we have described this invention as being particularly expedient with alpha fiber, and more especially alpha fiber in tissue form,

we desire to have it understood that fibers of other origin, e. g., sulphite or cotton fiber and in a form other than tissue, may be conditioned as herein described. For instance, fiber in a shredded condition may be passed in relatively thin layers through calender rolls, to effect a compacting or flattening of the shreds and to produce what is, in eflect, compacted, individual, small pieces of paper. Or

a loose and more or less flufiy web may be compacted or condensed by passage through calender rolls. In such cases, the air voids or interstices between the fibers are decreased to produce a less absorptive cellulosic material which is more suitable for nitration.

Having thus described the nature of our invention, it is evident that various changes might be resorted to without departing from the spirit or scope of invention as set forth in the appended claims.

What we claim is:

1. A process which comprises water-finishing an unsized paper, and then nitrating the same.

2. A process which comprises calendering a tissue of cellulosic fibers, and then dry crinkling the same while retaining the compactness produced by calendering.

3. A process which comprises calendering a tissue of cellulosic fiber, crinkling the tissue, and nitrating the same. 0

4. A process which comprises calendering a waterleaf tissue of high alpha cellulose wood fiber, crinkling the tissue, and nitrating the same.

5. A crinkled, calendered waterleaf tissue composed of wood pulp of an alpha cellulose content of at least about 93%.

6. A crinkled, calendered, and mercerized waterleaf tissue composed of high alpha cellulose wood fiber.

7. A process which comprises treating a tissue of cellulosic fiber with a cellulose derivative, and calendering the same.

8. A process which comprises treating a tissue of cellulosic fiber with a cellulose derivative, calendering the tissue, and then nitrating the same.

9. A process which comprises treating a tissue of cellulose fiber with a cellulose derivative, regenerating the cellulose fromthe derivative, and calendering the tissue.

10. A process which comprises treating a tissue with a cellulose derivative, regenerating the cellulose from the derivative, calendering the tissue, and then nitrating the same.

11. A calendered tissue composed of cellulose fiber permeated with a cellulose derivative.

12. A calendered tissue composed of cellulose fiber permeated withregenerated cellulose.

13. A process which comprises calenderin a waterleaf paper in moist condition, an then nitrating the same.

14. A process which comprises hot-calendering a waterleaf paper in moist condition, and then nitrating the same.

15. A calendered, mercerized waterleaf tissue composed of cellulose fibers.

16. A calendered, mercerized waterleaf tissue composed of high alpha cellulose wood signatures.

GEORGE A. RICHTER. MILTON O. SCHUR. ROYAL H. RASCH. 

